1. Field of Invention
This invention pertains to magnetic tape drives, and particularly to controlling slack tape developing during tape extraction and tape retraction operations.
2. Related Art and Other Considerations
In magnetic recording on tape using a magnetic tape drive, relative motion between a head unit (typically with both a write element and a read element) and the tape causes a plurality of tracks of information to be transduced with respect to the tape. The magnetic tape is typically housed in a cartridge which is loaded into the tape drive. The tape extends between a cartridge supply reel and a cartridge take-up reel. The tape drive typically has a supply reel motor for rotating the cartridge supply reel and a take-up reel motor for rotating the cartridge take-up reel.
After the cartridge is loaded into the tape drive, the tape is extracted by mechanisms in the drive so that a segment of the tape is pulled from the cartridge and into a tape path that travels proximate the head unit. The extraction mechanisms take the form of tape guides which are mounted on trolleys. During the extraction operation, trolley motors move the trolleys along a predefined trolley path, so that the tape guides which surmount the trolleys displace the tape into the tape path as the trolleys travel along the trolley path. When the trolleys reach the full extent of travel along the trolley path, the tape is proximate the head unit. Thereafter the tape can be transported past the head unit, e.g., by activation of a capstan and/or the supply reel and take-up reel motors, depending upon the particular type of transport mechanisms employed. A capstanless tape drive, particularly a tape drive which utilizes helical scan recording, is shown in U.S. Pat. No. 5,602,694 for CAPSTANLESS HELICAL DRIVE SYSTEM to Robert J. Miles and James Zweighaft, which is incorporated herein by reference.
As the tape is transported past the head unit, information can be transduced to or from the tape by the tape drive in recording and reading operations, respectively. When the recording and/or reading operations are concluded, and before the cartridge can be unloaded from the drive, the tape must be retracted for return to the interior of the cartridge. Tape retraction is essentially the reverse of the tape extraction procedure described above.
There is a trend in the tape drive industry toward reduction in thickness and stiffness of magnetic tapes in order to meet the requirements for digital signal recording/reproducing. There is also a demand for greater speed of extracting and retracting of the tape. Both these demands greatly increase the risk of the tape being damaged during a load/unload operation.
A desirable feature in modern tape drives is an operation called "mid-tape load/unload". This operation allows the tape to be extracted without first rewinding back to the beginning of tape. The next time the tape is loaded, it will be ready to resume at the point where the previous read/write operation ended. Without mid-tape load/unload capability, the user or host must wait a significant amount of time for the tape to rewind back to the beginning of tape (BOT) before the tape can be ejected. The subsequent load would then involve searching out on tape to the location where the last operation was halted. This can be a time consuming task which significantly limits system performance.
Preventing tape damage during mid-tape load/unloads is critical since previously written data could be damaged to the point where it is no longer capable of being recovered. Tape damage during mid-tape load/unloads could also cause debris to be generated which can eventually clog the read/write heads on the scanner.
What is needed therefore, and an object of the present invention, is apparatus and method for controlling tape extraction and retraction operations in order reduce the likelihood of damaging tape.